Using a 40amp charger for an hour. Ok?

[Stu Jackson]

Originally Posted by hamburking

The only improvement to your plan would be to get AGM batteries. They will charger much quicker than lead acid...but when you consider cost, the old lead acid battery is still all most of us require.

Not true. The OP said he understands he can't get to 100% SOC and can live with 90% and will get plugged in sometimes.

AGMs suffer from not being kept fully charged as soon and as often as possible.

This is a recurring misjudgement of AGMs. We see it over and over again, and people spend 3X for them and kill them.

AGM Battery Issues (from Maine Sail)
AGM Batteries - Making The Choice - SailboatOwners.com

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries - SailboatOwners.com

Originally Posted by hamburking

And finally, if you have two banks, or just two batteries, get 2 chargers...one charger on each battery. You'll get a better, faster charge than doing them together, plus you have a reduntant backup.

Not necessarily. Just wire the two banks together when charging. If you have the SAME daily load on any bank, consisting of either 1 or two batteries, the charging time will be pretty much the same, you're replacing the same amount of amp hours, right? Sure a larger proportion of charge into a smaller bank may go quicker, but it's peanuts in the big scheme of things.

[Reichberger]

To answer your question whether you can charge for an hour?

1. Note: these formulae: Watts = volts x amps Amps = watts/ volts Volts = watts/amps.
(Therefore for your generator producing 12 volts (I assume) at 900 watts substituting into the formulae Amp = 900/12 = 75 Amps. )The generator can cope with the demands of the battery charger.

2. I assume the battery (ies) are 12V. You have one or several?? If several they are either connected in series which makes their voltage additive 6V + 6V = 12V OR they are connected in parallel in which case the voltage stays the same and the amperage increases e.g. two 12 V 100 Amp hour batteries in parallel produce 12V at 200 Amp hours. In England batteries are quoted at the C10 rate (10 amps for 10 hours) and in the US at the C20 rate for amp hour-age. You must know the amp hours of the battery(ies) being charged.

3. Batteries do not like large deep cycles of charge/re-charge and if you wish them to last 2- 5 years if they are lead acid type then the maximum discharge is 50% of their amp-hours and re-charge to 80% of their amp-hours (as the last 20% takes a long time.) Therefore the maximal viable amps one can safely (for longevity of the battery) draw from the 100 Ahr battery is 30% (or 33 Amps 80%-50% = 30%)

4.A 'Smart' regulator regulates the charge rate by monitoring the voltage of the battery. It is programmed to break charging into three steps: Bulk charge; Absorption charge and Float charge.

Bulk charge will occur between 14.2 to 14.4 volts (at constant current i.e. constant amps). This will be a safe maximum of 25% of the battery's capacity and never higher than 40% of the battery's capacity i.e. 25A or 40A in a 100 Amp hr battery. (NB. Running 40 amps in will not be for the best!)
Absorption (Acceptance)charge the charger switches to constant voltage (14.2 to 14.4 volts) and the battery accepts whatever the amperage is to maintain this voltage and will end at about 2% of the battery's amp-hour rating. AT its termination the battery will be very nearly fully charged.
Float charge the regulator trips to a lower constant voltage setting 13.2 - 13.6V to prevent the battery overcharging.

Assuming you have a battery capacity of 100 Amp hours and its 12V run it down to 12.35 Volts i.e. 50% discharged connect the Smart charger and check when the voltage is 12.8V 80% charged. These readings need to be taken when the charger is disconnected from the battery and it has been allowed to settle. (It takes time for the chemicals to percolate through the cells (a delayed reaction).
By timing this process you will answer your question.

By constructing a large bank of batteries (400 -800 Amp hours capacity)and keeping to the 50% - 80% discharge/charge parameters with a high rate charge alternator (100 Amp - 200 Amp) one can obtain a surprising amount of amp hours for relatively little charging time.

I wish you all the best,

Erich

[Stu Jackson]

Originally Posted by Reichberger

To answer your question whether you can charge for an hour?

1. Note: these formulae: Watts = volts x amps Amps = watts/ volts Volts = watts/amps.
(Therefore for your generator producing 12 volts (I assume) at 900 watts substituting into the formulae Amp = 900/12 = 75 Amps. )The generator can cope with the demands of the battery charger.

I think the generator is 120V 7.5 amps

[tat]

Thank you all very much for that info, which collectively has settled my mind. I will get the honda gen, and a 40amp charger,, and I will monitor the state of the batteries very much, and I will give them a charge to keep them to 90%.

It is hard to believe we are still mucking about with lead acid heavy batteries in this day and age, because reliable and cost efficient. But then it is all part of the fun. But this way i will have what I need.

It is all a bit new to me. The batteries are about 100ah, and I have two (the outboard has its own). It is really just for the TV. It sounds bad that, but I just mean the weather report, the odd documentary, a film, and just the general comfort of a bit of telly, a sort of morale thing to keep all happy.

Electricity is the big concern, because everything else I can do in other way, like if I run out of propane for cooking, I can use a little camping spirit stove, and then there are candles.......it is just the telly, there is no way round it, ha, ha.

But thank you all very much. You could have said, STOP RIGHT THERE!!!!!!. DO NOT CHARGE AT 40AMPS OR YOU WILL EXPLODE THE BATTERY, YOURSELF, AND THE BOAT TO SMITHEREENS!

So I feel a bit more confident now. Thanks.

[onestepcsy37]

We do pretty much what you want to do. A honda eu1000 and a 35 amp smart charger. We have a 450ah battery bank. Every 3 days or so I put a quart of fuel in the honda and let it run until its out of gas. Works well and without the cost and complexity of an onboard charger. From my experience you should have no trouble using a 40 amp charger.

BTW, if its just for a tv I think you are wasting your money. Get a solar panel with a solar controller instead.

[Wotname]

Originally Posted by tat

Thank you all very much for that info, which collectively has settled my mind. I will get the honda gen, and a 40amp charger,, and I will monitor the state of the batteries very much, and I will give them a charge to keep them to 90%.

It is hard to believe we are still mucking about with lead acid heavy batteries in this day and age, because reliable and cost efficient. But then it is all part of the fun. But this way i will have what I need.

It is all a bit new to me. The batteries are about 100ah, and I have two (the outboard has its own). It is really just for the TV. It sounds bad that, but I just mean the weather report, the odd documentary, a film, and just the general comfort of a bit of telly, a sort of morale thing to keep all happy.

Electricity is the big concern, because everything else I can do in other way, like if I run out of propane for cooking, I can use a little camping spirit stove, and then there are candles.......it is just the telly, there is no way round it, ha, ha

But thank you all very much. You could have said, STOP RIGHT THERE!!!!!!. DO NOT CHARGE AT 40AMPS OR YOU WILL EXPLODE THE BATTERY, YOURSELF, AND THE BOAT TO SMITHEREENS!

So I feel a bit more confident now. Thanks.

Please be aware that although you have a 40 amp charger, the batteries will not be charging at 40 amps.

The charger has the capacity to deliver 40 amps, ie that is is maximum rated output.

But your batteries won't accept that much current. They will only accept what their chemistry and state of charge will allow them to accept. With about 200 AH of FLA and say 50% SOG, the acceptance current will be way less. Even if the intial acceptance current is near 40 amps (which I doubt), it will rapidily drop off as the SOG increases.

EDIT: you mentioned in your first post that you thought the your charger was not a "smart" charger however if it is, reread Erich's post #17, especially the difference of bulk and absorption charges ( ie constant current and constant voltage) . I have assumed you charger is simple, ie constant voltage.

[hamburking]

Originally Posted by Stu Jackson

Not necessarily. Just wire the two banks together when charging. If you have the SAME daily load on any bank, consisting of either 1 or two batteries, the charging time will be pretty much the same, you're replacing the same amount of amp hours, right? Sure a larger proportion of charge into a smaller bank may go quicker, but it's peanuts in the big scheme of things.

In theory you are correct. But in reality batteries do not conform to the theoretical numbers. I switched to a 2 charger system, and get a better, faster charge. I understand the theory, but I'm speaking from personal experience...it really works better. Each battery gets the full current it needs, and one battery does not buffer the other. No two batteries are identical, and when you connect them in parrallel, one is always boosting the other. The bulk of the charge goes to the weaker battery, and the stronger battery gets less. In a 2 charger system, they both get charged no matter what.

Have you ever had a dud/dead battery...connecting that to a good battery will just drain the good battery, really quick too. I'm saying that every battery is somewhere in the grey zone between good and dead, hopefully closer to good, but most boaters I know keep their batteries long after they have past their optimum performance.

If you check your water levels, you'll see that the cells nearest the positive connection to the charger will boil down fastest. Thats because that cell is charged first, then overcharged as the other cells are still trying to catch up. Its not as perfect as the math would have us think.

[sailinglegend]

Originally Posted by Stu Jackson

Overcharging with Combiners or ACRs The MYTH:
Overcharging Batteries with a Combiner or ACR

I don't normally challenge posts by Maine Sail but you might like to check with him if this OLD post is still absolutely accurate and worth linking to. See latest Maine Sail postings.

He of course is absolutely right about the starter battery will not be "overcharged" by too much current when combined because it will take ONLY the current it needs depending on its SoC. But if the starter battery is left combined when it's already at 100% SoC and it stays at a voltage ABOVE its gassing voltage for too long, then that voltage will cause excessive gassing and water loss. This is disastrous for sealed leisure batteries.

So “overcharging” should really be defined as “too high a voltage for too long”! That is why a multi-stage charger drops down to a float voltage after a certain time to “avoid overcharging the battery”. All multi-stage charger manufacturers say the same thing, and one battery manufacturer has this as part of his battery warranty when using multi-stage chargers.

Now to challenge Maine Sail’s “Myth Busting” example of a starter battery being charged for 2800 engine hours by a dumb regulated alternator with a combiner with absolutely no problems. These old regulators may only output 14 volts or less, way below the battery gassing voltage. His recent internet posts reveal how dumb the new alternators seem to be. They may be regulated at 14.6v but can quickly fall below 14v because of their internal temperature compensation. This is not that “Dumb” because they are reducing the voltage as the engine heats up because they assume that the batteries are also near the engine, the same way a charger with a battery temperature compensation sensor reduce the charging voltage to avoid gassing. This is why his starter battery wasn't overcharged for 5 years, and why car batteries are never “overcharged” even when driven for very long hours because the charging voltage is never above the gassing voltage long enough to cause excess gassing.

[colemj]

Our start batteries are combined with the house during charging, using solar and generator running a 120A charger, and rarely with the alternators (which do provide 14.8V throughout a charge cycle).

These start batteries spend a lot of time in absorption charge voltages, where I measure tenths of amps going into them when the charger is putting out 90A at >14.4V.

The original set of car battery type sealed FLA start batteries lasted 14 years (during which we went through 3 sets of house batteries). The replacement ones are only 4 years old, but show no signs of being damaged from holding at higher voltages with a combiner.

Mark

[sailinglegend]

Originally Posted by colemj

...These start batteries spend a lot of time in absorption charge voltages, where I measure tenths of amps going into them when the charger is putting out 90A at >14.4V......The replacement ones are only 4 years old, but show no signs of being damaged from holding at higher voltages with a combiner...

I agree with you, my sealed Red Flash starter battery is 10 years old.

It's all a matter of degree, how long fully charged at absorption voltage? Even a multi-stage chargers will drop down to a Float voltage maybe 3 hours after it has finally reached 14.4 volts. 24 hrs motoring with a starter battery at 100% and at 14.4v will not be good for it - I don't think that can be argued with.

I was trying to clarify the point about alternators not being able to overcharge a battery because they don't and can't stay at 14.4v all day and night.

[Stu Jackson]

The ENTIRE concept is based on, as included in that link: PROPER voltages. Why would one charge above gassing voltages for the house bank for any extended period of time? Once bulk is over, acceptance reduces the voltage, right?

And your discussion of dumb alternator regulators only pertains to Hitachi.

Originally Posted by sailinglegend

I don't normally challenge posts by Maine Sail but you might like to check with him if this OLD post is still absolutely accurate and worth linking to. See latest Maine Sail postings.

He of course is absolutely right about the starter battery will not be "overcharged" by too much current when combined because it will take ONLY the current it needs depending on its SoC. But if the starter battery is left combined when it's already at 100% SoC and it stays at a voltage ABOVE its gassing voltage for too long, then that voltage will cause excessive gassing and water loss. This is disastrous for sealed leisure batteries.

So “overcharging” should really be defined as “too high a voltage for too long”! That is why a multi-stage charger drops down to a float voltage after a certain time to “avoid overcharging the battery”. All multi-stage charger manufacturers say the same thing, and one battery manufacturer has this as part of his battery warranty when using multi-stage chargers.

Now to challenge Maine Sail’s “Myth Busting” example of a starter battery being charged for 2800 engine hours by a dumb regulated alternator with a combiner with absolutely no problems. These old regulators may only output 14 volts or less, way below the battery gassing voltage. His recent internet posts reveal how dumb the new alternators seem to be. They may be regulated at 14.6v but can quickly fall below 14v because of their internal temperature compensation. This is not that “Dumb” because they are reducing the voltage as the engine heats up because they assume that the batteries are also near the engine, the same way a charger with a battery temperature compensation sensor reduce the charging voltage to avoid gassing. This is why his starter battery wasn't overcharged for 5 years, and why car batteries are never “overcharged” even when driven for very long hours because the charging voltage is never above the gassing voltage long enough to cause excess gassing.

[sailinglegend]

Originally Posted by Stu Jackson

The ENTIRE concept is based on, as included in that link: PROPER voltages. Why would one charge above gassing voltages for the house bank for any extended period of time? Once bulk is over, acceptance reduces the voltage, right?

And your discussion of dumb alternator regulators only pertains to Hitachi.

Sorry Stu but I think you are confused!

During the Bulk stage the voltage slowly rises to the Absorption Voltage. This is the "gassing voltage" that a battery needs to reach to gas a little to stir up the electrolyte and even out the acid distribution. It stays at this gassing voltage (Absorption) for a time that is set by the charger. This can be custom set to stay longer if you have a large bank, and some "Smart Chargers" may calculate how long to stay there based on how long it took to get to the "Absorption Voltage" in the first place. So a fully charged battery may drop to Float in less than 5 minutes. In Absorption the battery accepts less and less current but the voltage stays the same.

Hitachi are NOT the only dumb alternators, only the ones Maine Sail has talked about.

I have a new marine "Hot Rated" Balmar 6 series alternator with a standard internal auto regulator set at 14 volts. It's wired to switch quickly to the internal regulator if the external Balmar regulator fails. On internal it very quickly drops to 13.7 volts under high charge current so I emailed Balmar and asked why a hot rated alternator should do this. I quote Balmar's email:

"There are two temperature compensation schemes:

A few internal regulators will reduce the alternator output and voltage based upon the internal alternator temperature in order to protect the alternator.
The second is monitoring the temperature of the battery so the regulator can adjust the voltage to ensure the battery is being charged at the optimal voltage and not gas the battery or under charge the battery. Our regulators have both features as options, alternator temperature sensing to protect the alternator and battery temperature sensing to monitor the battery temperature in order to optimally charge the battery."